This invention relates generally to hydraulic shock absorbers and more particularly to hydraulic shock absorbers that dissipate the kinetic energy of an automotive suspension system.
Conventional hydraulic shock absorbers work in a damping range which is a compromise between suspension control and ride comfort. In the past this compromise has been addressed by adjusting damping levels in various ways.
For example, in a known semi-active suspension system, the hydraulic shock absorber has a by-pass channel between the upper or rebound chamber of the pressure tube and the reservoir of the shock absorber that is controlled by a solenoid valve that is computer actuated in response to suspension conditions to provide two discrete damping levels. When open the solenoid valve allows hydraulic fluid escaping the rebound chamber to bypass the piston valve assembly so that the shock absorber provides a low damping force or soft mode of operation. However, when the solenoid valve is closed, the escaping hydraulic fluid cannot bypass the piston valve assembly so that the shock absorber provides a high damping force or firm mode of operation in the rebound direction. See for instance, the shock absorber that is shown and described in connection with FIGS. 41-43 of U.S. Pat. No. 4,650,042 granted to Heinz Knecht et al Mar. 17, 1987 for an adjustable hydraulic shock absorber.
Adjustable hydraulic shock absorbers, such as those exemplified by the Knecht et al patent, provide satisfactory operation under many conditions. However, certain events, such as a vehicle driving off a curb or squared edge, are too fast for these computer controlled shock absorbers to sense and react to in time to dissipate the excessive suspension energy.